私有综合服务网络（PISN）是一种专用的通信网络，通常用于企业内部通信。PISN可以提供多种服务，如电话、传真、电子邮件等。为了实现这些服务，PISN需要一种互换信令协议，以便不同的设备和系统之间进行通信。

ISO/IEC 20117:2004标准定义了一种互换信令协议，以便在不同的PISN之间进行通信。该协议包括消息中心监控和邮箱识别的补充服务。消息中心监控服务允许用户监控消息中心的状态，包括已接收的消息数量、未读消息数量等。邮箱识别服务允许用户识别邮箱的类型和状态，如语音信箱、传真信箱等。

ISO/IEC 20117:2004标准的主要目的是提供一种标准化的方法，以便在不同的PISN之间进行通信和交换信息。该标准可以帮助企业和组织实现更高效、更可靠的通信，同时降低通信成本和维护成本。

相关标准
- ISO/IEC 11572:1995 Information technology — Telecommunications and information exchange between systems — Private Integrated Services Network — Inter-exchange signalling protocol — Call transfer supplementary service
- ISO/IEC 11574:1995 Information technology — Telecommunications and information exchange between systems — Private Integrated Services Network — Inter-exchange signalling protocol — Call diversion supplementary service
- ISO/IEC 11582:1995 Information technology — Telecommunications and information exchange between systems — Private Integrated Services Network — Inter-exchange signalling protocol — Call hold supplementary service
- ISO/IEC 11583:1995 Information technology — Telecommunications and information exchange between systems — Private Integrated Services Network — Inter-exchange signalling protocol — Call waiting supplementary service
- ISO/IEC 11584:1995 Information technology — Telecommunications and information exchange between systems — Private Integrated Services Network — Inter-exchange signalling protocol — Call completion supplementary service